1. Field of the Invention
The present invention relates generally to a rotary feed mechanism for intermittently driving a shaft in response to repeated turn of an operating element and, in particular but not exclusively, to the rotary feed mechanism for use suitably in incrementally adjusting the height of an automobile seat assembly above an automobile in-compartment floor in response to reciprocate turn of a seat adjustment handle between a neutral position and one of highest and lowest positions opposite to each other with respect to the neutral position.
2. Description of the Related Art
The use of the rotary feed mechanism in automobile seat height adjustment has been well known and is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2000-118273. This known rotary feed mechanism is used in combination of a seat height adjustment mechanism including a pair of parallel link mechanisms that are driven in unison with each other to elevate or lower the automobile seat assembly relative to the automobile in-compartment floor. The rotary feed mechanism disclosed therein is used to drive the parallel link mechanisms in unison with each other for the intended purpose and includes an operating lever or handle pivotally mounted on one of opposite side seat frames on which a seat cushion is fixedly mounted, for movement between a neutral position and one of highest and lowest positions corresponding respectively to the highest and lowest available seat positions above the automobile in-compartment floor. When the operating lever is turned repeatedly from the neutral position towards the highest or lowest position, the seat cushion can be elevated or lowered incrementally, respectively.
The known rotary feed mechanism is interposed between the axis of pivot of the operating lever and a drive shaft drivingly coupled with one of the parallel link mechanisms and also includes a one-way brake drum carried by that one of the side seat frames and having input and output shafts, and a ratchet mechanism operatively intervening between the brake drum and the operating lever. The brake drum is designed to allow the output shaft to rotate only in response to rotation of the input shaft in either one of directions opposite to each other, but to prevent the input shaft from rotating in response to a force acting on the output shaft to rotate the output shaft. The output shaft of the brake drum may either be the drive shaft for driving one of the parallel link mechanisms or be drivingly coupled with such drive shaft.
The ratchet mechanism referred to above includes a ratchet gear fixedly mounted on the input shaft for rotation together therewith and a pair of ratchet paw) members that are selectively brought into engagement with the ratchet gear one at a time, depending on whether the operating lever is turned from the neutral position towards the highest position or whether it is towards the lowest position, so that the pivot of the operating lever can be transmitted to the input shaft.
In order to elevate or lower the automobile seat cushion a maximum available distance towards the highest or lowest available seat position, the operating lever has to be repeatedly turned in forward-going and rearward-going directions from the neutral position towards the highest or lowest positions to incrementally elevate or lower the seat cushion. While the forward-going turn of the operating lever results in engagement of one of the ratchet pawl members with one of gear teeth of the ratchet gear to thereby rotate the ratchet gear in response to the forward-going turn of the operating lever, the rearward-going turn of the operating lever as biased by a biasing spring used to return and hold the operating lever to the neutral position allows the respective ratchet pawl member to override some of the gear teeth of the ratchet gear while clicking those gear teeth one after another until the operating lever returns to the neutral position, accompanied by generation of obnoxious clicking noises. The clicking noises are indeed harsh and uncomfortable to hear.
The present invention has been developed to overcome the above-described disadvantages and is intended to provide an improved rotary feed mechanism which is substantially free from generation of the obnoxious noises and which can be assembled with a minimized number of component parts.
In order to accomplish the foregoing object, the present invention provides a rotary feed mechanism which includes a brake drum having input and output shafts and operable to drivingly couple the input and output shafts together to rotate the input and output shafts in unison with each other only when the input shaft is driven regardless of the direction in which the input shaft is rotated; an operating lever mounted on the input shaft of the brake drum and supported for rotation from a neutral position in first and second directions opposite to each other about a longitudinal axis of the input shaft; and a ratcheting mechanism intervening between the operating lever and the brake drum and operable to permit rotation of the input shaft only when the operating lever is angularly moved from the neutral position in any one of the first and second directions, but to lock the input shaft during angular movement of the operating shaft back to the neutral position. The ratcheting mechanism in turn includes a lock gear having gear teeth and mounted on the input shaft for rotation together therewith; an indexing plate movable angularly between an engaged position, in which the indexing plate is engaged with some of the gear teeth of the lock gear, and a disengaged position, in which the indexing plate is disengaged from some of the gear teeth of the lock gear, about an axis lying substantially perpendicular to a longitudinal axis of the input shaft, and a release mechanism carried by the brake drum for releasing the indexing plate from the engaged position to allow the operating lever to be returned to the neutral position.
According to the present invention, since the lock gear is positioned externally of the brake drum and the movement of the indexing plate between the engaged and disengaged positions takes place in a direction generally perpendicular to the input shaft, there is no way of the indexing plate overriding some of the gear teeth during the return movement of the operating lever back to the neutral position while clicking those gear teeth one after another until the operating lever returns to the neutral position. Accordingly, the rotary feed mechanism according to the present invention is substantially quiet and substantially free from generation of the obnoxious clicking noises.
In one preferred embodiment of the present invention, the rotary feed mechanism preferably includes a biasing spring for normally urging the indexing plate to the engaged position to allow the angular movement of the operating lever to be transmitted to the input shaft through the lock gear. In this case, the release mechanism being operable against the biasing spring to release the indexing plate. The indexing plate may be supported by the operating lever by means of a support shaft defining such axis substantially perpendicular to the input shaft and has an array of parallel catch slots defined therein for engagement with some of the gear teeth of the lock gear. The release mechanism preferably includes a guide means for guiding the indexing plate to permit some of the gear teeth to be engaged in the corresponding catch slots during the angular movement of the operating lever in one of the first and second directions from the neutral position, but to be disengaged from the catch slots during the angular movement of the operating lever back to the neutral position.
In another preferred embodiment of the present invention, the indexing plate has a finger extending therefrom in a direction laterally of a plane of rotation of the lock gear and towards the release mechanism. The guide means includes a second biasing spring, a cam element urged in one direction by the second biasing spring and pivotable against the second biasing spring upon engagement with the finger during the angular movement of the operating lever from the neutral position to permit the indexing plate to be angularly moved from the engaged position, said first cam member being returned back to an initial position by the second biasing spring in response to return of the operating lever back towards the neutral position, and a guide element engageable with the finger during a return movement of the operating lever back to the neutral position to keep the indexing plate at the disengaged position. The second biasing spring preferably has a biasing force greater than that of the first biasing spring.
In any event, the rotary feed mechanism of the present invention can be used in association with a seat height adjusting mechanism for adjustably elevating or lowering a seat assembly relative to a floor. In this case, the output shaft of the brake drum is drivingly coupled with the seat height adjusting mechanism.